The present invention relates to a device for determining the mass flow and direction of flow of a fluid of substantially directed flow with known mass flow, having a mass-flow measuring device provided with a thermoelectric mass-flow sensor and a temperature sensor and having at least one temperature-measuring element.
The fuel injection of internal combustion engines is controlled as a function of the mass flow of the intake air. For the measurement of the mass flow, use is made in many cases of a mass-flow measuring device which operates in accordance with the electrothermal principle. Such a measuring device is provided with at least one temperature sensor in order to compensate for the temperature, and with a mass-flow sensor the main component of which is an electrically heatable resistance element located in the mass flow. The heat removed from this heating element is a measure of the mass flow, more heat being removed the stronger the mass flow is.
Such a mass-flow measuring device is very insensitive with respect to the direction of the flow, since, regardless of whether the flow is directed forward or backward, practically the same electric signal is given off corresponding to the heat removed. In other words, with a known mass-flow measuring device one can merely determine the amount of mass flow but not its direction. It has now been found that, in the intake system of internal combustion engines, under certain operating conditions, oscillations of the air column occur and are superimposed on the constant flow so that a rapidly pulsating flow results therefrom. Depending on the revolutions per minute and the number of cylinders, the fundamental frequency of the oscillation is within the range of between 10 and 1000 Hertz. Depending on the velocity of flow and the amplitude of oscillation, reverse flows take place for short periods of time. In view of the above-described principle of measurement of the massflow measuring device, reverse flow produces the same measurement signal as intake flow, so that, in the final analysis, too large an amount of fuel is fed to the engine.
Direction-sensitive flow meters are known which have two resistance elements arranged on a common support member, the resistance elements being installed one behind the other in the direction of flow. Such prior-art flowmeters, however, are not suitable for detecting rapid changes in flow because of their inertia.